Proportioned air control for refrigerator-freezer



June 25, 1968 E. H. FROHBIETER 3,389,575

PROPORTIONED AIR CONTROL FOR REFRIGERATOR-FREEZER Filed March 1, 1967 il- [28 l /54' u 1;.5 0 4- 24 INVENTOR r, I L? I 4 Enwm \-\.'FRQ\\B\ETER BY j d M ATTORNEY United States Patent 3,389,575 PROPORTIONED AIR CONTROL FOR REFRIGERATOR-FREEZER Edwin H. Frollbieter, Stevensville, Mich., assignor to Whirlpool Corporation, Benton Harbor, Micl1., a corporation of Delaware Filed Mar. 1, 1967, Ser. No. 619,683 Claims. (Cl. 62-190) ABSTRACT OF THE DISCLOSURE A combination refrigerator-freezer of the forced air type having an air duct for by-passing a varying portion of air around an evaporator in response to frost build up on the evaporator. Frost build up on the evaporator is accompanied by a decrease in the temperature and volume of the main stream of air which requires that a greater proportion of the available air be provided to the refrigerator in order to maintain a desired constant temperature diflerential between the refrigerator and freezer compartments. The by-passed air is directed into the main stream of air leaving the evaporator adjacent a divider Wall separating air ducts leading to the refrigerator and freezer compartments. The impinging stream of by-passed air alters the course of the main stream of air to effect a desired proportioning of the main stream of air between the refrigerator and freezer compartments, which proportion varies in response to frost build up on the evaporator.

Background of invention The invention described herein is preferably utilized in a combination refrigerator-freezer of the type having a single evaporator for chilling air, which air is then supplied to above and below freezing compartments by way of ducting, the air being moved through the ducting by air translation means such as a fan or blower. This type of apparatus comprises a refrigerator or above-freezing compartment and a freezer or below-freezing compartment, with the volumetric capacity of the above-freezing compartment being greater than the volumetric capacity of the below-freezing compartment. A remote evaporator is in fluid communication with the compartments through a ducting system which provides a circuitous flow path for air whereby the air within the compartments may be continuously circulated past the evaporator.

The air translation means is arranged in the ducting system to force air past the evaporator and to circulate the air through the system. In this well-known type of system, water vapor is picked up by the circulating air from foods stored in the compartments and also as a result of relatively moist air entering the compartments when the doors thereof are opened. A portion of this water vapor is deposited by condensation on the evaporator as the air within the system is circulated past the evaporator. The condensate freezes on the cold surfaces of the evaporator and causes frost to build up. As frost accumulates on the evaporator, the cross sectional area of the ducting is reduced at the evaporator and a corresponding resistance to air flow develops at the evaporator. With increased resistance to air flow the volume of air flowing in the system per unit of time is reduced and the temperature of the air leaving the evaporator decreases. Thus, a typical system operates under gradually varying conditions of volumetric air flow and air temperature.

Temperature control of this type of refrigeration system is usually effected by a thermostat located in the above freezing compartment. For example, a thermostat may be set for a controlled temperature of 40 F. in the refrigerator. The ducting for the system is then balanced to deliver, under no frost conditions, a sufiicient volume 3,389,575 Patented June 25, 1968 of cold air to the refrigerator to maintain a temperature of 40 F. While supplying the freezer with a volume of air sufficient to maintain a temperature of, for example 5 F. Freezer temperature control may be accomplished by providing an adjustable baffle in the refrigerator supply air passage. The bafile controls the amount of available air which enters each of the compartments so that a constant thermostat setting the freezer temperature may be varied by varying the amount of air supplied thereto. While this system is balanced at the desired temperature (e.g., 40 F. for the refrigerator and 5 F. for the freezer) under no frost conditions, as the evaporator frosts the system gradually becomes unbalanced in operation. The unbalance under frosted conditions can be acceptable in some respects because in order to satisfy the cooling requirements of the refrigerator the cooling apparatus can be called upon to operate for longer intervals which will cause the temperature of the freezing compartment to be lowered in relation to the constant temperature of the refrigerator.

However, it is preferred to maintain constant and optimum temperatures in both compartments, because constant temperature conditions give the most efficient operation of the apparatus and optimum temperaures are desirable from the standpoint of food storage life and food quality.

A primary object of this invention is to provide an improved control apparatus for a combination refrigeratorfreezer unit whereby a relatively constant temperature differential may be maintained between the refrigerator and freezer sections of the unit.

Another object of the invention is to provide a combination refrigerator freezer wherein cooling air is apportioned between the refrigerator and freezer sections as a function of the frost condition of the evaporator.

Another object of the invention is to provide a forced air combination refrigerator-freezer having means for bypassing a variable portion of the air around the evaporator and back into the main stream of air leaving the evaporator to cause a varying deflection of the main stream of air and apportioning of air between air ducts leading to the refrigerator and freezer compartments.

Other objects and advantages of the invention will be obvious to those skilled in the art after reading the following description in conjunction with the drawings wherein:

Description of the invention FIGURE 1 is a perspective view of an evaporator housing showing the air duct arrangement of the present invention. Portions of the housing are removed to illustrate the arrangement of parts within the housing;

FIGURE 2 is a diagrammatic plan view of the evaporator housing of FIGURE 1 showing the air flow paths through the housing;

FIGURE 3 is a diagrammatic front elevational view of a combination refrigerator-freezer with the doors removed to show the arrangement of air ducts in the apparatus;

FIGURE 4 is a sectional view taken along lines 4--4 of FIGURE 3; and

FIGURE 5 is a fragmentary sectional view taken along the lines 5-5 of FIGURE 2 with parts broken away to illustrate details.

Referring now to the drawings in which like reference numbers refer to like parts in the several figures, a combination refrigerator-freezer generally designated 10 in FIGURE 3 comprises a thermally insulated cabinet 12 defining an above freezing refrigerator compartment 14 having a control thermostat 15 located therein and a below freezing freezer compartment 16. The doors to close compartments 14 and 16 have been omitted from FIGURE 3 to show the interior arrangement. A refrigeration apparatus compartment indicated at 18 is provided for housing a conventional refrigeration system comprising a compressor, a condenser, and an evaporator. The compressor and condenser are not shown since they are conventional and form no part of the invention. An air duct means generally indicated at is provided for circulating air between compartments 14 and 16 and an evaporator 22 disposed in compartment 18 (FIGURE 4). Duct means 20 comprises a supply duct 24 including a branch portion 26 for supplying air to freezer compartment 16 and a branch portion 28 for supplying air to refrigerator compartment 14. An adjustable air baffle 29 is provided in branch portion 28 for effecting freezer temperature control by blocking air flow to refrigerator compartment 14. If less air is permitted to enter compartment 14, the freezer temperature will decrease. Duct means 20 further includes a return air duct 30 (FIGURE 3) for returning air from compartments 14 and 16 to evaporator 22. The apparatus thus far described is conventional and those skilled in the art will recognize other conventional modifications therein which in no way limit the scope of the invention hereinafter described.

Referring now to FIGURES 1 and 2, an evaporator housing generally designated 32 comprises air outlet member or supply duct 24, and an air inlet member 34 which communicates with return air duct 30. Inlet member 34 further communicates with a blower housing 38 through an opening in the blower housing. A conventional blower 39 is contained within the blower housing 38 and is arranged to draw air through return duct 30, inlet member 34, and opening 40 in a well-known manner and force or blow the air through the evaporator housing 32. Air flow through the evaporator housing is illustrated by arrows in FIGURES 1 and 2. From the blower the air is directed toward the front of housing 32 by way of a passage 42 defined by the top, bottom, and left side walls of housing 32 and wall member 44 within housing 32. From the front of the evaporator housing the air is directed rearwarclly over evaporator 22 as indicated by the arrows in FIGURE 2 and out of evaporator housing 32 through outlet member 24. The top, bottom, and right side walls of evaporator housing 32 and a wall member 46 (FIGURE 1) thus form an air passage within housing 32. An air fiow passage 48 (FIGURES 1 and 2) is defined by the top and bottom walls of housing 32 and walls 44 and 46. Passage 48 communicates with a duct 50 which directs air from passage 48 into outlet member 24. Air from duct 50 is directed into outlet member 24 through a narrow slot-like opening 52 formed in outlet member 24. Opening 52 is preferably substantially coextensive in width with outlet member 24, and is the point at which duct 50 has a minimum cross sectional area. The air from duct 50 is directed into outlet member 24 immediately adjacent a divider wall 54 (FIG- URES 2 and 5). Air passage 48 and duct 50 thus serve as conduit means to bypass a portion of the air delivered by the blower which would otherwise pass through evaporator 22. Located in passage 48 is an evaporator header or accumulator 56 for cooling bypassed air.

In operation, air is circulated to the refrigerator and freezer compartments through evaporator 22 by blower 39. Referring to FIGURES 1, 4 and 5 it will be seen that air leaving evaporator 22 enters supply duct 24 and fiows upwardly to where the air stream is split by divider Wall 54. With the air stream split, a portion of the air flows through branch portion 26 of the supply duct 24 to freezer compartment 16 and a portion of the air flows through branch portion 28 to refrigerator compartment 14. In addition to the air flowing through evaporator 22, a small portion of the air leaving blower 39 flows through passage 48 and duct 50 and is delivered through opening 52 into the main air stream leaving evaporator 22. This bypass air stream is preferably directed substantially perpendicularly into the main air stream and serves to alter or deflect the course of the main air stream as a function of the velocity of the bypass air stream. Alternatively the bypass air may be directed into the main stream of air at an angle to the perpendicular. When the bypass air stream is directed upwardly toward divider wall 54, there is in addition to the deflecting effect previously mentioned an entraining efiect which tends to draw main stream air into the bypass air stream.

It will be appreciated that the divider wall 54 may be located to provide division of the air stream to give a desired initial cooling capacity for each of the storage compartments 14 and 16. However, as previously described, the air fiow and air temperature conditions in this type of apparatus will not remain constant due to frost build up on the evaporator. As frost builds up on the evaporator, the circulating air meets an increasing resistance to flow through the evaporator which results in a decrease in volumetric air flow through the evaporator. The temperature of the air leaving the evaporator also decreases due to longer contact with evaporator surfaces and a decrease in evaporator temperature. With a decrease in volumetric air flow through the evaporator there is a corresponding increase in volumetric air flow through the bypass passage 48 and duct 50, because of relatively less resistance to fiow in the bypass path. An increase in volumetric air flow in the bypass path results in an increased velocity of the bypass air stream. This will increase the diverting effect of the bypass air stream on the main air stream and a larger proportion of the available air leaving the evaporator housing will enter branch portion 28 of supply duct 24 to be delivered to the refrigerator compartment. The volume of air which is bypassed is very small compared to the volume of air in the main stream of air so that the temperature of the resulting mixture of air is not appreciably affected by the addition of warmer bypass air. In addition, the evaporator header 56 is located in the passage 48 to provide some cooling of the bypass air.

For the purposes of illustrating the need for supplying a greater proportion of cooling air to the refrigerator compartment as the temperature of the supply air decreases, a simple calculation may be made by selecting two sets of conditions and solving for the ratio of air volumes necessary to effect the desired cooling for each of the compartments under each set of conditions.

Example The temperature to be maintained in the refrigerator compartment is 40 F. and the temperature to be maintained in the freezer compartment is 5 F. Now assume that the amount of cooling necessary to maintain the above temperatures is equal. The cooling efi ect obtained from the supply air is proportional to the volume of air supplied to a compartment times the change in temperature in that air as it passes through the compartments. The temperature of the supply air under the first set of conditions is 0 F. Then equating the cooling effects necessary for maintaining the desired refrigerator and freezer temperatures as assumed, the equation V Al :V At is obtained, where V =volume of air supplied to the refrigerator compartment;

V =volume of air supplied to the freezer compartment;

At =temperature change of supply air in the refrigerator compartment; and

At =temperature change of supply air in the freezer compartment.

Then solving the equation for the ratio of V to V When the evaporator begins to be plugged by frost buildup, the temperature of the supply air decreases. For example, the temperature of the supply air may drop to F. Now, again solving the equation for supply air at a temperature of -10 F., we obtain Thus as the temperature of the supply air decreases, at greater proportion of the available air must be supplied to the refrigerator compartment in order to maintain a constant temperature differential between the compartments. While the assumption was made that each compartment required the same amount of refrigeration or cooling, it will be apparent that the volumetric ratio of air required to maintain given compartment temperatures will vary in the same manner for different ratios of required refrigeration.

Since the decrease in temperature of the supply air and the increase in the volume of the bypass air are both proportional to frost build up on the evaporator, it will be seen that the invention provides a means for automatically compensating for the continually varying air flow and air temperature conditions which are typical for the type of refrigeration apparatus described.

Thus, as frost builds up on the evaporator and the temperature of the supply air decreases, an increasing volume of air will be bypassed to deflect an increasing proportion of supply air to the refrigerator compartment as required.

While I have shown and described one embodiment of the invention, it will be understood that modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In forced air refrigeration apparatus having at least two compartments to be maintained at predetermined different temperatures by cold air supplied at a single temperature:

the improvement comprising, first duct means for conveying a stream of cold air to said compartments, said first duct means including a wall means defining branch portions, one branch portion leading to each of said compartments;

air cooling means for cooling air to be conveyed to said compartments;

second duct means for returning air from said compartments to said air cooling means;

air translation means for focing air over said air cooling means and thence to said branch portions; and

conduit means providing communication between said first and second duct means for bypassing a varying quantity of air around said air cooling means in response to build up of frost on said air cooling means, said conduit means being arranged to direct said bypassed air into said first duct means to cause a desired proportioning of said stream of cold air between said branch portions, thereby to maintain said predetermined different temperatures in said compartments when said air cooling means is partially blocked by frost build up on said air cooling means.

2. The refrigeration apparatus of claim 1 including second air cooling means in said conduit means.

3. The refrigeration apparatus of claim 2 wherein said second air cooling means is an elongated refrigerant header having a longitudinal axis parallel to the direction of air flow in said conduit means.

4. The refrigeration apparatus of claim 1 wherein said conduit means is disposed to direct said bypassed air perpendicularly into said stream of air.

5. The refrigeration apparatus of claim 1 wherein said conduit means is arranged to direct said bypassed air into said stream of air adjacent said wall means.

6. The refrigeration apparatus of claim 1 wherein said conduit means defines a narrow slot-like opening in said first duct means.

7. The refrigeration apparatus of claim 6 wherein said narrow slot-like opening is substantially coextensive in width with said first duct means.

8. The refrigeration apparatus of claim 1 wherein said air cooling means is controlled by a thermostat located in one of said two compartments.

9. The refrigeration apparatus of claim 8 wherein said thermostat is located in the compartment to be maintained at the highest of said different temperatures.

10. The refrigeration apparatus of claim 1 wherein said wall means is a divider wall common to said branch portions.

References Cited UNITED STATES PATENTS 2,812,642 11/1957 Jacobs 62-4l9 2,939,296 6/ 1960 Coblentz 2-419 3,020,733 2/1962 Hubacker 62-419 3,050,956 8/1962 Mann 62-4l9 3,299,664 1/1967 Booth 62-4l9 WILLIAM J. WYE, Examiner. 

